Applicant claims the priority of Japanese patent application, Ser. No. 11-102,293, filed Apr. 9, 1999.
The present invention relates to a fuel jet supporting structure in a carburetor, and more particularly to a supporting structure for a fuel jet which is provided in a fuel passage communicating a fuel tank with an air intake passage in a carburetor of a fixed vacuum slidable throttle valve type or the like.
As shown in FIGS. 3 and 4, a conventional fuel jet supporting structure in a carburetor comprises a support column 15 which projects from a lower end of a carburetor body 2 into a fuel tank 45. A fuel in the fuel tank 45 is adapted to be delivered through a fuel jet body 25 which is engaged in a fuel passage 24 formed through the support column 15 to an air intake passage 9. The fuel jet body 25 is provided at its middle portion with a fuel jet 30 for controlling the amount of the fuel flow. The fuel jet body 25 also has a plurality of radially extending holes 29 formed at its forward end portion downstream of the fuel jet 30. The air passage bore 19 communicates with the atmospheric chamber 4 through an air introducing passage 13 which is closed at an end by a ball 10, a vertically extending air inducing passage 8, and an air jet 6. The fuel is mixed with an air from the air passage bore 19 and supplied to the air intake passage 9 through an outlet passage bore 16 and passage 12 which open to air intake passage 9.
A tapered bore 20 is formed at a stepped portion between the air passage bore 19 and a threaded bore 41. A tapered shaft portion 40 of the fuel jet body 25 is engaged in the tapered bore 20 in order to prevent the fuel from leaking to the air passage bore 19 without passing through the fuel jet 30. In order to provide an airtight seal between the air passage bore 19 and the outlet passage bore 16, a projecting rib 39 having a triangular cross-section and formed at the forward end of the fuel jet body 25 is adapted to be tightly engaged in the outlet passage bore 16.
However, because the projecting rib 39 is rotatingly press-fitted into the outlet passage bore 16 with a threaded portion 41a of the fuel jet body 25 screwed into the threaded bore 41, the outlet passage bore 16 is likely to be deformed. Consequently, the degree of precision varies in producing the outlet passage bore 16 and thus the airtighteness between the outlet passage bore 16 and the projecting rib 39 can become deteriorated. Accordingly, there is a problem that air from the passage 13 passing into the outlet passage bore 16 may not enter into the interior of an emulsion tube 26 but instead flow into the outlet passage bore 16 through a gap between the outlet passage bore 16 and the projecting rib 39 resulting in instability of the flow rates of both the fuel and the air.
What is needed is a fuel jet supporting structure in a carburetor which has an improved seal between the inlet and the outlet of the air passage bore.
In accordance with the present invention, a fuel jet supporting structure includes a support column projecting from a bottom of a carburetor body into an interior of a fuel tank and provided with a fuel passage which introduces a fuel from within the fuel tank to an air intake passage in the carburetor body. The fuel jet supporting structure has the fuel passage and a fuel jet body received therein. The fuel passage includes a fuel passage bore receiving the fuel jet body, an air passage bore communicating with an air introducing passage of the carburetor body, a threaded bore, and an outlet passage bore which are formed in the support column downstream from the threaded bore and preferably having a diameter smaller than the threaded bore. A stepped portion of the bore lies between the threaded bore and the outlet passage bore. Preferably, this stepped portion of the bore is tapered.
The fuel jet body includes a fuel jet provided at a middle part of a fuel passage passing through the fuel jet body. An emulsion tube is formed with a plurality of radially extending holes and provided at an axial portion within the air passage bore. A threaded portion is adapted to engage with the threaded bore at its downstream portion, and a stepped shaft portion abuts against the stepped portion of the bore. Preferably, the stepped shaft portion at its downstream end face is tapered with the complementary shape of the taper of the stepped portion of the bore.
According to the invention, the fuel jet body is provided with the threaded portion at the downstream portion. The tapered shaft portion of the fuel jet body is rigidly engaged in the tapered bore which is formed in the outlet passage bore downstream of the air passage bore. Further, the fuel jet body is preferably provided with an O-ring upstream of the emulsion tube and inserted in the fuel passage bore in the support column. Thus, the air passage bore is reliably sealed at both upstream and downstream sides, and all the fuel in the fuel tank enters into the emulsion tube through the fuel jet to be mixed with the air, and flows into the outlet passage bore, whereby a stable flow rate of the fuel is achieved.